Equipping internal combustion engines, in particular internal combustion engines for motor vehicles, with one or more exhaust gas sensors is generally known. The exhaust gas sensors are typically connected to a control and/or regulating unit of the internal combustion engine, so that the control and/or regulating unit may detect information about the composition of exhaust gases exiting from combustion chambers of the internal combustion engine. Typically at least one lambda sensor, which may be used to detect an oxygen concentration in the exhaust gas, is provided as an exhaust gas sensor in an internal combustion engine. This allows a conclusion to be drawn about an air/fuel ratio in the combustion chamber, so that the internal combustion engine may be regulated in such a way, for example, that emission regulations are met.
The lambda sensors may be divided into so-called bistable sensors and broadband sensors. The broadband sensors may in turn be designed to be single-cell broadband sensors or to be dual-cell broadband sensors. A bistable sensor has a rather high sensitivity for an excess-air ratio of the exhaust gas which is in the range of λ=1. For excess-air ratios which are not in the range of approximately λ=1, the sensitivity of the bistable sensors is relatively low. Therefore, in the case of a continually rising excess-air ratio in the exhaust gas, a jump of an output signal generated by a bistable sensor results as soon as the excess-air ratio enters the range of approximately λ=1. In contrast, broadband lambda sensors have a relatively high sensitivity also outside the range of the excess-air ratio around the value λ=1.
Modern internal combustion engines typically have one or two lambda sensors, bistable and/or broadband sensors being used for gasoline engines. Diesel engines predominantly have broadband lambda sensors.
During operation of the internal combustion engine, the control and/or regulating unit detects sensor signals which are generated by the lambda sensor or the lambda sensors and additional sensors of the internal combustion engine and operates the internal combustion engine as a function of these sensor signals. In order to be able to recognize errors in the sensors, the control and/or regulating unit checks the individual sensor signals during the operation of the internal combustion engine. In this case, the signals are typically checked as to whether electrical errors (e.g., short-circuits or line interruptions) exist. For this purpose, for example, it may be checked whether the sensor signals are in permissible value ranges. In addition, the control and/or regulating unit typically checks whether there are system errors. A system error is recognized, for example, if the variables detected with the aid of different sensors contradict one another. If the control and/or regulating unit recognizes an electrical error and/or a system error, it registers the occurrence of the error in an error memory.
Known diagnostic methods, which are performed, for example, to prepare for repairs or during maintenance work on the internal combustion engine or on a motor vehicle in which the internal combustion engine is installed, resort to the information stored in the error memory, for example. In this way, conclusions about the functionality of a lambda sensor may be drawn to a certain extent. Since there are complex interactions between various components of the internal combustion engine during operation of the internal combustion engine, however, a sufficiently secure and reliable diagnosis of an individual lambda sensor is not possible. For example, if an electrical error is recognized, it typically cannot be reliably established whether the error is based on a defect of the lambda sensor or whether the control and/or regulating unit, in particular an analysis circuit for the sensor signals of the lambda sensor, is defective. In addition, in many cases system errors may not be definitely assigned to a specific sensor, for example, a specific lambda sensor. The risk exists that the lambda sensor will be incorrectly recognized as defective, although in actuality another component of the internal combustion engine is not functioning correctly, in particular another sensor of the internal combustion engine. If a defect occurs in the internal combustion engine, cumbersome error searches may therefore occur if known diagnostic methods are used, until the actually defective component is finally identified. Reliable conclusions about the type of the error of the lambda sensor are practically impossible to be drawn in the case of known diagnostic methods.
Single-cell and dual-cell broadband lambda sensors are discussed, for example, in DE 10 2006 014 266 A1. Furthermore, detecting a leakage current between an electrode of the lambda sensor and a heating element of the lambda sensor is discussed in DE 197 16 173 A1.